1. Field of the Invention
The invention relates to a method for producing titanium particles suitable for use in powder metallurgy applications. The particles are formed by inert gas atomization of molten titanium.
2. Description of the Prior Art
In various titanium, powder metallurgy applications, such as the manufacture of jet engine components, it is desirable to produce spherical titanium particles that may be subsequently hot compacted to form fully dense articles. Compacting is generally achieved by the use of an autoclave wherein the titanium particles to be compacted are placed in a sealed container, heated to elevated temperature and compacted at a high fluid pressure sufficient to achieve full density. For these applications, it is desirable that the titanium particles be spherical to ensure adequate packing within the container which is essential for subsequent hot compacting to full density. Nonspherical powders, when hot compacted in this manner, because of their low packing density, result in distortion of the exterior source of the compact. As described in U.S. Pat. No. 4,544,404 issued Oct. 1, 1985, it is known to produce spherical titanium particles for powder metallurgy applications by gas atomization of a free-falling stream of molten titanium metered through a nozzle of a tundish. With these practices, the titanium may be melted to form the required molten mass by practices including nonconsumable electrode melting of a solid charge of titanium.
In these conventional practices for inert gas atomization of titanium to form particles suitable for powder metallurgy applications, the melting practice employed, such as nonconsumable electrode melting, can result in contamination of the molten mass by the electrode material. In addition, to provide the controlled, free-falling stream required for effective atomization, metering through a nozzle is required. Consequently, the nozzle must be monitored to ensure that plugging of the nozzle or erosion of the nozzle do not significantly affect the metering of the stream of molten titanium to adversely affect inert gas atomization thereof. If the free-falling stream becomes greater than required, the atomization will not be complete to result in an excess amount of oversized, insufficiently cooled particles. On the other hand, if the stream is less than required, the molten titanium will freeze in the nozzle.